Let us now consider the simple but still not-trivial Witten diagram shown in the figure REF .The simplest not trivial diagram corresponds to a 4-point contact diagram., corresponding to a single scalar exchange. We will use this example to illustrate the approach we are going to use in the following over more complicated examples.
This diagram was previously computed long time ago in [1]} and later revisited in [2]} by means of the split-representation which we will review in the appendix A.
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